The present invention relates to the field of Integrated Services Digital Network User Part (ISUP) signaling, and more particularly to the processing and routing of ISUP signaling messages within a switching system.
Signaling is the process of transferring information to control the setup, holding and releasing of connections in a communications network. The network may be a public telephone network or a switched private telephone network. In a network, signaling may be divided into two parts: customer line signaling and inter-office trunk signaling. Customer line signaling refers to the interaction between a telephony agent and the switching system serving the customer. Interoffice trunk signaling is concerned with the exchange of call-handling information between switching offices within a network.
Today, communications networks commonly use two types of signaling techniques: traditional in-band signaling and out-of-band signaling. For traditional in-band signaling, signaling information is transmitted on the same wire or trunk and follows the same transmission path as the call itself. For out-of-band signaling, signaling information pertaining to a call is transmitted on a separate dedicated facility known as a signaling link.
Signaling System 7 (SS7) is an industry standard for out-of-band signaling in a communications network. In a SS7 network, signaling information is carried in packets between switching systems in much the same manner as X.25 or other packet switching protocols. An SS7 network provides increased bandwidth for call signaling and increased capability for providing advanced network services across different network platforms.
The SS7 protocol is comprised of four layers. Layers 1, 2 and 3, collectively referred to as the Message Transfer Part (MTP), provide the basic infrastructure for transporting signaling messages across the SS7 network. MTP is compliant with layers 1, 2 and 3 of the Open System Interconnection (OSI) standard. Layers 1, 2 and 3 of OSI are defined in ITU-T X.200.
Layer 4 of the SS7 protocol consists of three parts: Signaling Connection Control Part (SCCP), Integrated Services Digital Network User Part (ISUP), and Transaction Capability Application Part (TCAP). SCCP provides additional routing and network management services to MTP. TCAP provides connectionless communications between applications on a network using a generic standard language.
ISUP provides connection-oriented signaling between nodes on a communications network. This type of signaling provides the capability to set up and take down calls and to monitor the facilities on which calls are transported. Furthermore, ISUP is a service-rich protocol which provides the capability to communicate large amounts of information associated with calls over signaling links. This service-rich aspect of the ISUP protocol is particularly attractive to telephone service providers because it supports advanced network services such as, caller ID, call screening, and automatic recall, across different switching systems and telephony agents.
ISUP signaling protocol is defined in GR-246-CORE, xe2x80x9cBellcore Specification of Signaling System 7xe2x80x9d, Volume 3, American National Standards Institute (ANSI) T1.113-1988, and International Telecommunications Unionxe2x80x94Telecommunication Standardization Sector (ITU-T) Q.761, Q.762, Q.763, Q.764, Q.766, xe2x80x9cSpecifications of Signalling System No. 7 ISDN User Part.xe2x80x9d
A telephone switching office which supports SS7 signaling is referred to as a Service Switching Point (SSP). Each switching office is assigned a unique point code for the purpose of identifying the office in the telephone network. Typically, a switching office includes a switching system which is connected to switching systems in other switching offices via inter-office trunks.
A trunk for which ISUP signaling information is handled on a separate signaling link is referred to as an ISUP trunk. An ISUP trunk that originates from and terminates at the same SSP is referred to as an ISUP loopback trunk. The point at which a trunk originates from a switching system is referred to as a near endpoint, and the point at which a trunk terminates at a switching system is referred to as a far endpoint.
FIG. 1 shows the external interfaces of a prior art switching system. Switching system 100 is connected to user terminals 115, 136, and 138 via customer lines 114, 135, and 137 respectively. User terminal 115 is a standard plain ordinary telephone service (POTS) telephone, user terminal 136 is a fax machine, and user terminal 138 is an ISDN terminal that includes a video machine and a POTS telephone.
Switching system 100 interfaces with ISUP loopback trunks 110 and ISUP inter-office trunks 111. ISUP loopback trunks 110 originate from and terminate at switching system 100. ISUP inter-office trunks 111 connect switching system 100 to switching system 150. Switching system 100 has a plurality of digital trunk controllers which interface with ISUP loopback trunks 110 and ISUP inter-office trunks 111. Signaling links 112 connect switching system 100 to SS7 network 113. Switching system 100 has a plurality of signaling terminals which interface with signaling links 112.
Switching system 150 is connected to user terminals 160, 170 and 180 via customer lines 155, 165 and 175 respectively. User terminal 160 is a standard plain ordinary telephone service (POTS) telephone, user terminal 170 is an ISDN terminal that includes a video machine and a POTS telephone, and user terminal 180 is a desktop computer system.
Switching system 150 has a plurality of digital trunk controllers which interface with ISUP inter-office trunks 111. Signaling links 140 connect switching system 150 to SS7 network 113. Switching system 150 has a plurality of signaling terminals which interface with signaling links 140.
Switching system 100 processes ISUP signaling messages 120 which are associated with ISUP inter-office trunks 111 and routes them to and from signaling links 112. Because the far endpoints of ISUP inter-office trunks 111 terminate at switching system 150, ISUP signaling messages 120 travel through the SS7 network 113 and arrive at switching system 150.
Switching system 100 also processes ISUP signaling messages 130 which are associated with ISUP loopback trunks 110 and routes them to signaling links 112. Because the far endpoints of ISUP loopback trunks 110 terminate at switching system 100, ISUP messages associated with ISUP loopback trunks 110 travel through SS7 network 113 and arrive back at switching system 100.
Routing ISUP signaling messages associated with ISUP loopback trunks to the SS7 network presents a unique challenge for switching systems because a switching system cannot use a single point code to identify itself as both the source and the destination when routing these messages. Specifically, most switching systems detect and disallow circular routing of signaling messages to the SS7 network (i.e., the source and destination being the same SSP). To get around this problem, telephone service providers must assign an additional point code to each SSP. However, assigning an additional point code to each SSP creates extensive network management problems because in a communications network each SSP must be identified by a unique point code.
Furthermore, in the case of ISUP loopback trunks, ISUP signaling messages must be processed by the MTP layer of the SS7 protocol in switching system signaling terminals, even though the source and the destination of the messages are the same. The main purpose of the MTP layer is to provide reliable transport for signaling messages within the SS7 network, and thus, it is unnecessary for a switching system to send these messages to the SS7 network when they are destined for that same switching system.
To take advantage of the advanced services of the MTP layer, telephone service providers must allocate the resources of switching system signaling terminals to ISUP loopback trunks as well as ISUP inter-office trunks. In the case of ISUP loopback trunks, the MTP layer processing associated with ISUP signaling messages in signaling terminals is an unnecessary overhead because the source and the destination for ISUP messages in the SS7 network are the same. Consequently, there has been a long felt need in the industry for a switching system that would eliminate the routing of ISUP signaling messages associated with ISUP loopback trunks to the SS7 network.
One known solution is to hardwire the ports of switching system signaling terminals together so that ISUP signaling messages associated with ISUP loopback trunks are routed from one signaling terminal to another within the switching system. While this solution eliminates transmission of ISUP signaling messages to the SS7 network by looping together signaling terminals, it has several disadvantages. Most notably, telephone service providers must still allocate the resources of signaling terminals to ISUP loopback trunks, and thus, increasing switching system costs. Furthermore, telephone service providers must assign an additional point code to each SSP. Moreover, the MTP layer processing associated with ISUP signaling messages is not eliminated. Finally, hardwiring of signaling terminals requires manual intervention by switching office technicians to pre-allocate signaling terminal ports to ISUP loopback trunks, and thus, increasing operational costs.
Another known solution is to process and route the ISUP signaling messages associated with ISUP loopback trunks within a switching system, thus, eliminating the processing of these messages in switching system signaling terminals. This solution also has several drawbacks. In particular, it uses a proprietary intra-switch messaging protocol which routes ISUP messages within the switching system to the far endpoint trunks. However, because of the rising demand in the industry for an open interface for communication among switching systems in the network, a proprietary messaging protocol would make it more difficult for telephone service providers to integrate such switching systems into their networks.
Therefore, it is desirable to provide a method and a system for processing ISUP signaling messages associated with ISUP loopback trunks within a switching system using an open standard protocol that supports all of the services of the ISUP layer of the SS7 protocol, eliminates the use of signaling terminals for these types of trunks and reduces SS7 network congestion, switching system costs and operational costs.
The present invention is directed to a method and an apparatus for processing ISUP signaling messages associated with loopback trunks within a switching system using an open standard that supports all of the services of the ISUP layer of the SS7 protocol. Because ISUP messages are routed within the switching system, telephone service providers need not purchase additional signaling terminal hardware and software to support the signaling traffic associated with loopback trunks, thereby reducing costs. Moreover, depending upon the configuration of the switching system, the number of ISUP signaling messages in the SS7 network, and thus network congestion, can be reduced. Furthermore, to support ISUP signaling, telephone service providers can assign a single point code to each SSP, thereby eliminating network management problems associated with the assignment of multiple point codes. Finally, because the processing associated with the MTP layer of the SS7 protocol is eliminated, the performance of ISUP signaling is enhanced for ISUP loopback trunks.
Specifically, the present invention comprises a method for processing within a switching system ISUP signaling messages associated with an ISUP loopback trunk by provisioning the ISUP loopback trunk, identifying the ISUP signaling messages associated with the ISUP loopback trunk, and routing the identified ISUP signaling messages within the switching system to the far endpoint of the ISUP loopback trunk using layers 1, 2 and 3 of Open System Interconnection (OSI) protocol.
This invention further comprises a communications network that includes a first and a second switching system, a first trunk interconnecting the first switching system to the second switching system, a second ISUP trunk with two endpoints that originate from and terminate at the first switching system, where the first switching system has means for identifying the ISUP signaling messages that are associated with the second ISUP trunk, and means for routing the identified ISUP signaling messages to the far endpoint of the second ISUP trunk using layers 1, 2 and 3 of the OSI protocol.
The invention further comprises a computer-readable medium capable of configuring a switching system to perform a method of processing ISUP signaling messages within the switching system. The method includes the steps of provisioning an ISUP loopback trunk that has two endpoints which originate from and terminate at the switching system, identifying the ISUP signaling messages that are associated with the ISUP trunk, and routing the identified ISUP signaling messages to the far endpoint of the ISUP loopback trunk using layers 1, 2 and 3 of the OSI protocol.
The summary and the following detailed description should not restrict the scope of the claimed invention. Both provide examples and explanations to enable others to practice the invention. The accompanying drawings, which form part of the detailed description, show several embodiments of the invention, and together with the description, explain the principles of the invention.